1. Field of the Invention
The present invention relates to a process for surface treatment of moldings of melt-processable polyester resin capable of forming an anisotropic molten phase (abbreviated as "liquid-crystalline polyester" hereinafter). More particularly, it is concerned with an efficient process for surface treatment of moldings of liquid-crystalline polyester having superior heat resistance and moldability, said process being intended to provide the moldings with surface characteristics suitable for surface decoration such as printing, painting, metallizing, and plating and also for bonding with an adhesive.
2. Description of the Prior Art:
A liquid-crystalline polyester is composed of rigid, straight macromolecules unlike commonly known thermoplastic polyesters such as polybutylene terephthalate and polyethylene terephthalate. The macromolecules remain straight, with only a few entanglements, even in the molten state; therefore, they easily orient in one direction when subjected to even a small shear stress. Thus the liquid-crystalline polyester remains in the crystalline state even in the molten state or exhibits the properties of liquid crystal.
The above-mentioned liquid-crystalline polyester is chemically stabler than the common polyester resins (such as polybutylene terephthalate and polyethylene terephthalate) which do not exhibit the properties of liquid crystal. Therefore, it is not receptive to an etching solution used for the surface roughening of ordinary polyester. Even though the surface roughening is achieved in some way, the roughened surface does not have a sufficient activity for the catalyst solution for plating and hence does not undergo the subsequent electroless plating successfully. No satisfactory method has been developed yet.
The liquid-crystalline polyester may be processed by injection molding which is in general use. However, the injection-molded products have a surface layer which easily peels off and fluffs on account of strong orientation. Thus, they are not suitable as such for the secondary fabrication such as bonding, painting, and plating. A possible remedy for this is the surface roughening treatment with a chemical which is applied to ordinary resins. Unfortunately, the surface to be treated is so chemically inactive that it does not receive any solvent. Thus it is virtually impossible to remove the oriented surface layer and to make a roughened surface.
On the other hand, the liquid-crystalline polyester has unique thermal characteristics. That is, it has a low coefficient of linear expansion comparable to that of metals, and it remains normal even when dipped in a solder bath at 260.degree. C. for 10 seconds on account of its good heat resistance. Because of these outstanding characteristics, the liquid-crystalline polyester is expected to find use as parts to be bonded to a metal part with an adhesive or as printed-circuit boards to be plated. Such parts and PC boards need surface treatment to remedy the above-mentioned disadvantageous surface characteristics. Nevertheless, no satisfactory process has been established yet.